H.264/AVC 利用可變區塊大小(variable block size) 的動作預估 (motion estimation)和編碼率失真最佳化(rate-distortion optimized) 的區塊模式選擇 (macroblock mode decision) 達到極高壓縮效果，但是暴力的區塊模式檢查過程花費了整個壓縮過程大部分的計算量。為了要降低這部份的計算量，許多論文提出了加速模式選擇的演算法，卻忽略了前景、背景和區塊模式間的關係。
本篇論文提出了基於背景模型的模式選擇演算法：我們首先利用本質影像技術產生背景資訊，根據背景資訊，每個宏塊 (macroblock) 將會背歸類到三種前景、背景的宏塊類型當中，每種類型將會指定使用不同的候選區塊模式。區塊模式的編碼率失真值 (rate-distortion cost) 將成為剔除不必要的模式檢查的比較基準。另外，背景資訊也會用來加速動作預估。本論文也提出一個依QP值不同而改變的臨界值，當做提早結束區塊模式選擇的標準。
實驗結果顯示，平均而言本論文可以加速50%的編碼時間，而只造成少部分的失真率下降以及編碼率提高。另外，我們也試著探究影像中真正的運動區域，同時也維持了前景部分的影像品質。

H.264/AVC utilizes variable block size motion estimation and rate distortion optimized mode decision to achieve high coding efficiency. However, the exhaustive mode checking procedure takes up most part of the computational load. To reduce the computational complexity, many works focus on expediting the mode decision process but are not aware of the relationship between the foreground/background and the chosen mode. In this thesis, we propose a background-modeling-based fast mode decision algorithm which will first generate the background information using intrinsic image technique. According to the background information, macroblocks are classified into three foreground/background macroblock types which will be assigned different candidate modes. Rate-distortion cost will be the comparison to skip unnecessary block mode checking, and with the assistance of background information, fast motion estimation mechanism is proposed. We also use a QP dependent threshold value as an early termination yardstick. The experimental results demonstrate that the proposed algorithm reduces, on average, 48% of the entire encoding time with negligible PSNR drop and bit-rate increase. Moreover, we endeavor to find out the true motion in the video sequences, while retaining the foreground quality.

[1] Draft ITU-T Recommendation and Final Draft International Standard of Joint Video Specification, ITU-T Rec. H.264 and ISO/IEC 14496-10 AVC, Joint Video Team, Mar. 2003.
[2] Y. W. Huang, B. Y. Hsieh, S. Y. Chien, S. Y. Ma, and L. G. Chen, "Analysis and complexity reduction of multiple reference frames motion estimation in H.264/AVC," IEEE Transactions on Circuits and Systems for Video Technology, vol. 16, no. 4, pp. 507-522, April 2006.
[3] Y. Su and M. T. Sun, "Fast multiple reference frame motion estimation for H.264," in IEEE International Conference on Multimedia and Expo (ICME), June 2004, pp. 695-698 Vol.1.
[4] Y. Su and M. T. Sun, "Fast multiple reference frame motion estimation for H.264/AVC," IEEE Transactions on Circuits and Systems for Video Technology, vol. 16, no. 3, pp. 447-452, March 2006.
[5] B. Feng, G. X. Zhu, and W. Y. Liu, "Fast adaptive inter-prediction mode decision method for H.264 based on spatial correlation," in IEEE International Symposium on Circuits and Systems (ISCAS), September 2006, pp. 1804-1807.
[6] C. J. Duanmu and X. Chen, "Fast motion estimation mode decision algorithm for H.264/AVC video coding standard," in Asia Pacific Conference on Postgraduate Research in Microelectronics & Electronics (PrimeAsia), January 2009, pp. 313-316.
[7] F. Pan, X. Lin, S. Rahardja, K. P. Lim, Z. G. Li, D. Wu, and S. Wu, "Fast mode decision algorithm for intraprediction in H.264/AVC video coding," IEEE Transactions on Circuits and Systems for Video Technology, vol. 15, no. 7, pp. 813-822, July 2005.
[8] H. Wang, S. Kwong, and C. W. Kok, "An Efficient Mode Decision Algorithm for H.264/AVC Encoding Optimization," IEEE Transactions on Multimedia, vol. 9, no. 4, pp. 882-888, June 2007.
[9] H. Huang and D. Hu, "An Efficient Fast Inter Mode Decision Algorithm for H.264/AVC," in WRI International Conference on Communications and Mobile Computing (CMC), January 2009, pp. 161-165.
[10] H. Zeng, C. Cai, and K. K. Ma, "A Novel Fast Mode Decision for the H.264/AVC Based on Local Macroblock Motion Activity," in The Forth International Conference on Image and Graphics (ICIG), August 2007, pp. 263-267.
[11] H. Zeng, C. Cai, and K. K. Ma, "Fast Mode Decision for H.264/AVC Based on Macroblock Motion Activity," IEEE Transactions on Circuits and Systems for Video Technology, vol. 19, no. 4, pp. 491-499, April 2009.
[12] H. M. Wang, J. K. Lin, and J. F. Yang, "Fast H.264 Inter Mode Decision Based on Inter and Intra Block Conditions," in IEEE International Symposium on Circuits and Systems (ISCAS), May 2007, pp. 3647-3650.
[13] I. Choi, J. Lee, and B. Jeon, "Fast Coding Mode Selection With Rate-Distortion Optimization for MPEG-4 Part-10 AVC/H.264," IEEE Transactions on Circuits and Systems for Video Technology, vol. 16, no. 12, pp. 1557-1561, December 2006.
[14] J. M. Moon, Y. H. Moon, and J. H. Kim, "A Computation Reduction Method for RDO Mode Decision Based on an Approximation of the Distortion," in IEEE International Conference on Image Processing (ICIP), October 2006, pp. 2481-2484.
[15] J. Lee and B. Jeon, "Fast mode decision for H.264," in IEEE International Conference on Multimedia and Expo (ICME), June 2004, pp. 1131-1134.
[16] J. H. Kim and B. G. Kim, "Fast block mode decision algorithm in H.264/AVC video coding," Journal of Visual Communication and Image Representation, vol. 19, no. 3, pp. 175-183, April 2008.
[17] P. Gao, L. Shen, G. Teng, and J. Xie, "Fast Inter Mode Decision Algorithm Using Spatiotemporal Characteristic of Motion Vector Field," in Third International Conference on Convergence and Hybrid Information Technology (ICCIT), November 2008, pp. 912-918.
[18] T. Zhao, H. Wang, S. Kwong, and C. C. J. Kuo, "Fast Mode Decision Based on Mode Adaptation," IEEE Transactions on Circuits and Systems for Video Technology, vol. 20, no. 5, pp. 697-705, May 2010.
[19] W. S. Jang, J. Heo, and Y. S. Ho, "Efficient Selection of Candidates for Fast Inter Mode Decision in H.264," in Second International Conference on Future Generation Communication and Networking Symposia (FGCNS), December 2008, pp. 222-225.
[20] D. Wu, S. Wu, K. P. Lim, F. Pan, Z. G. Li, and X. Lin, "Block INTER mode decision for fast encoding of H.264," in IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), May 2004, pp. 181-184.
[21] X. Wang, J. Sun, Y. Liu, and R. Li, "Fast Mode Decision for H.264 Video Encoder Based on MB Motion Characteristic," in IEEE International Conference on Multimedia and Expo (ICME), July 2007, pp. 372-375.
[22] Y. C. Lin, T. Fink, and E. Bellers, "Fast Mode Decision for H.264 Based on Rate-Distortion Cost Estimation," in IEEE International Conference onAcoustics, Speech and Signal Processing (ICASSP), April 2007, pp. 1137-1140.
[23] Y. H. Haung, C. Y. Chang, and H. H. Chen, "Fast H.264 Mode Decision Using Previously Coded Information," in Tenth IEEE International Symposium on Multimedia (ISM), December 2008, pp. 82-88.
[24] Y. H. Huang, T. S. Ou, and H. H. Chen, "Fast H.264 selective intra mode decision for inter-frame coding," in Picture Coding Symposium (PCS), May 2009, pp. 1-4.
[25] Y. Huang, Q. Liu, and T. Ikenaga, "Macroblock feature and motion involved multi-stage fast inter mode decision algorithm in H.264/AVC video coding," in IEEE International Conference on Image Processing (ICIP), November 2009, pp. 1041-1044.
[26] Z. Liu, L. Shen, and Z. Zhang, "An Efficient Intermode Decision Algorithm Based on Motion Homogeneity for H.264/AVC," IEEE Transactions on Circuits and Systems for Video Technology, vol. 19, no. 1, pp. 128-132, January 2009.
[27] Z. Zhou, J. Xin, and M. T. Sun, "Fast motion estimation and Inter-mode decision for H.264/MPEG-4 AVC encoding," Journal of Visual Communication and Image Representation, vol. 17, no. 2, pp. 243-263, April 2006.
[28] H. Tang and H. Shi, "Fast Mode Decision Algorithm for H.264/AVC Based on All-Zero Blocks Predetermination," in International Conference on Measuring Technology and Mechatronics Automation (ICMTMA), April 2009, pp. 780-783.
[29] Y. Peng, H. Y. C. Tourapis, A. M. Tourapis, and J. Boyce, "Fast mode decision and motion estimation for JVT/H.264," in International Conference on Image Processing (ICIP), September 2003, pp. 853-856.
[30] T. Zhao, H. Wang, X. Ji, and S. Kwong, "Two-Dimensional Map Based Fast Mode Decision for H.264/AVC," in Proceedings of the 9th Pacific Rim Conference on Multimedia (PCM), 2008, pp. 148-157.
[31] C. H. Hsia, J. S. Chiang, Y. H. Wang, and T. Yuan, "Fast Intra Prediction Mode Decision Algorithm for H.264/AVC Video Coding Standard," in Third International Conference on Intelligent Information Hiding and Multimedia Signal Processing (IIHMSP), Novembor 2007, pp. 535-538.
[32] S. C. Hsia and Y. C. Chou, "Fast intra-prediction with near pixel correlation approach for H.264/AVC system," Image Processing, IET, vol. 2, no. 4, pp. 185-193, 2008.
[33] H. Zeng, K. K. Ma, and C. Cai, "Hierarchical Intra Mode Decision for H.264/AVC," IEEE Transactions on Circuits and Systems for Video Technology, vol. 20, no. 6, pp. 907-912, June 2010.
[34] T. Wiegand, H. Schwarz, A. Joch, F. Kossentini, and G. J. Sullivan, "Rate-constrained coder control and comparison of video coding standards," IEEE Transactions on Circuits and Systems for Video Technology, vol. 13, no. 7, pp. 688-703, July 2003.
[35] B. Zhan, B. Hou, and R. Sotudeh, "Temporal-Spatial Correlation Based Mode Decision Algorithm for H.264/AVC Encoder," in Forth IEEE International Symposium on Electronic Design, Test and Applications (DELTA), January 2008, pp. 351-355.
[36] J. Bu, S. Lou, C. Chen, and J. Zhu, "A Predictive Block-Size Mode Selection for Inter Frame in H.264," in IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), May 2006, pp. 917-920.
[37] D. Wu, F. Pan, K. P. Lim, S. Wu, Z. G. Li, X. Lin, S. Rahardja, and C. C. J. Ko, "Fast intermode decision in H.264/AVC video coding," IEEE Transactions on Circuits and Systems for Video Technology, vol. 15, no. 7, pp. 953-958, July 2005.
[38] Z. K. Lin, H. H. Lin, Y. H. Chen, and J. H. Chuang, "On the Performance Improvement of H. 264 Through Foreground and Background Analyses," in IEEE International Conference on Multimedia and Expo (ICME), July 2005, pp. 848-851.
[39] Y. Weiss, "Deriving intrinsic images from image sequences," in Eighth IEEE International Conference on Computer Vision (ICCV), July 2001, pp. 68-75.
[40] Joint Video Team Reference Software JM12.2 [Online]. Available: http://iphome.hhi.de/suehring/tml/download/old_jm/
[41] J. Sun, W. Zhang, X. Tang, and H. Y. Shum, "Background Cut," in European Conference on Computer Vision (ECCV), May 2006, pp. 628-641.